(a) Technical Field
The present disclosure relates to a device and method that improve stack performance of a fuel cell system, and more particularly, to a device and method that improve stack performance of a fuel cell system, which improves fuel efficiency by improving stack performance under a low-temperature and low-pressure operating condition.
(b) Background Art
Stack performance of a fuel cell system under a normal-pressure operating condition is rapidly changed due to a change in an outside environment (e.g., outside temperature, atmospheric pressure, etc.). In particular, as atmospheric pressure decreases, the stack performance rapidly deteriorates in proportion to the decrease in atmospheric pressure. A pressurized fuel cell system, which uses a compressor, may overcome the deterioration in stack performance by adjusting stack working pressure, but a normal-pressure fuel cell system, which has no pressure control hardware, adjusts an air amount by adjusting a flow rate, and thus a deterioration in performance according to pressure is unavoidable, as shown in FIG. 1A-1B of the related art.
The normal-pressure fuel cell system has advantages in that efficiency thereof is high since noise, instability, and power consumption of auxiliary machinery are low. However, a part of the normal-pressure fuel cell system that is vulnerable to working pressure causes deterioration in vehicle performance. As a result, a decrease in atmospheric pressure caused by an increase in altitude, which is one of the various environmental conditions of a vehicle, degrades stack efficiency and adversely affects fuel efficiency.
A fuel cell stack for a vehicle is typically required to be operable under various environments without degrading performance. The stack performance/efficiency changes in proportion to a change in pressure among the environmental conditions. Therefore, the fuel cell system in which a stack reaction is controlled based on the amount (e.g., mass) of air is vulnerable to a deterioration in stack performance which is caused by an increase in altitude above sea level (i.e., a decrease in atmospheric pressure).
Meanwhile, deterioration in vehicle performance under a high altitude condition is a phenomenon that may be found in a vehicle with an internal combustion engine. In the case of the internal combustion engine, the deterioration in performance may be prevented by high altitude compensation. In addition, even in the fuel cell system capable of adjusting air pressure, pressure compensation in response to the high altitude may be adjusted by forcedly increasing stack working pressure. However, this system has a drawback in that efficiency thereof is low, and loud noise is generated.
The above information disclosed in this section is merely for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.